The invention concerns a turbulence generator in the headbox of a paper or paperboard making machine, by whose means internal microturbulence is produced in the pulp suspension flow, whereby the homogeneity of the flow is improved, the turbulence generator comprising a system of turbulence tubes, which consists of a number of turbulence tubes placed one above the other and side by side, these tubes extending from an inlet side of said turbulence generator to an outlet side thereof and having at the inlet side a substantially circular cross-section, and being gradually and smoothly, in the flow direction, converted to a cell structure with planar sides, in which cellular structure, with the exception of any lateral ducts, the cross-sectional flow areas of each cell are substantially equal in size, as compared with one another, and which cell structure is substantially fully occupied at the outlet side of the turbulence generator.
As is known in the prior art, in various headboxes in paper machines, turbulence generators are used, in which the pulp suspension flow is distributed into turbulence tubes to make component flows, which are discharged at the outlet side of the turbulence generator into a discharge duct that becomes narrower in a wedge-shaped manner. Out of the discharge opening of the discharge duct, the pulp suspension jet is discharged onto a forming wire or into a forming gap defined by two opposite wires.
A type of headbox which is known from the prior art and is commonly used has a turbulence generator wherein there is first a perforated plate in the flow direction of the pulp suspension. This perforated plate comprises a large number of flow holes placed in a number of rows placed one above the other, these flow holes opening into turbulence tubes which are wider than the diameters of the holes. These turbulence tubes begin having a circular cross section coaxial with the flow holes in the perforated plates and turn somewhat towards one another in the vertical plane. By the time that the outlet said of the turbulence generator is reached, the turbulence tubes have changed smoothly to tubes of substantially square cross-section, so that they have vertical walls and horizontal walls. The tubes placed vertically one above the other are staggered relative to one another in such a way that the vertical walls of tubes placed one above the other have a certain angular shift relative to one another in the lateral direction.
It has been a drawback in prior art headboxes, for example in those described hereinbefore but also in other headboxes, that when using these headboxes striated paper is often produced wherein streaks occur in the transverse direction, generally with the same spacing as the spacing of the tubes of the turbulence generator. Moreover, by means of measurement, it has been possible to ascertain that, in the discharge duct in the headbox, variation occurs in the turbulence intensity and velocity profiles with the same tube spacing. This variation occurs in all of the layers of headbox flow placed one above the other, and this variation is at a maximum on and near the faces of the lower and upper walls of the discharge duct.